WebKit is a layout engine designed to allow web browsers to render web pages. WebKit powers the Apple Safari and Google Chrome browsers. As of 2012 it has the most market share of any layout engine at 36% of the browser market share according to StatCounter. It is also used as the basis for the experimental browser included with the Amazon Kindle ebook reader, as well as the default browser in the iOS, Android, BlackBerry Tablet OS and webOS mobile operating systems. The WebKit engine provides a set of classes to display web content in windows, and implements browser features such as following links when clicked by the user, managing a back-forward list, and managing a history of pages recently visited.

WebKit's HTML and JavaScript code originally began as a fork of the KHTML and KJS libraries from KDE,^[2] and has now been further developed by individuals from KDE, Apple Inc., Nokia, Google, Bitstream, RIM, Samsung, Igalia, and others.^[3] Mac OS X, Windows, GNU/Linux, and some other Unix-like operating systems are supported by the project.^[4]

WebKit's WebCore and JavaScriptCore components are available under the GNU Lesser General Public License, and the rest of WebKit is available under a BSD-form license.^[5]

Origins[link]

The code that would become WebKit began in 1998 as the KDE’s HTML layout engine KHTML and KDE's JavaScript engine (KJS). The WebKit project was started within Apple by Don Melton on 25 June 2001^[6] as a fork of KHTML and KJS. Melton explained in an e-mail to KDE developers^[7] that KHTML and KJS allowed easier development than other available technologies by virtue of being small (fewer than 140,000 lines of code), cleanly designed and standards-compliant. KHTML and KJS were ported to Mac OS X with the help of an adapter library and renamed WebCore and JavaScriptCore.^[7] JavaScriptCore was announced in an e-mail to a KDE mailing list in June 2002, alongside the first release of Apple's changes.^[8] WebCore was announced at the Macworld Expo in January 2003 by Apple CEO Steve Jobs with the release of the Safari web browser. JavaScriptCore was first included with Mac OS X v10.2 as a private framework which Apple used within their Sherlock application, while WebCore debuted with the first beta of Safari. Mac OS X v10.3 was the first major release of Apple's operating system to bundle WebKit, although it had already been bundled with a minor release of 10.2.

However, the exchange of code patches between the two branches of KHTML has previously been difficult and the code base diverged because both projects had different approaches in coding.^[9] One of the reasons for this is that Apple worked on their version of KHTML for a year before making their fork public.

Despite this, the KDE project was able to incorporate some of these changes to improve KHTML's rendering speed and add features, including compliance with the Acid2 rendering test.^{[citation needed]} Konqueror 3.5 passed the Acid2 test, which was released after Apple had opened its WebKit Concurrent Versions System (CVS) and Bug Database.

According to Apple, some changes involved Mac OS X–specific features (e.g., Objective-C, KWQ, Mac OS X calls) that are absent in KDE's KHTML, which called for different development tactics.^[10]

Split development[link]

At one point KHTML developers said they were unlikely to accept Apple's changes and claimed the relationship between the two groups was a "bitter failure".^[11] Apple submitted their changes in large patches that contained a great number of changes with inadequate documentation, often to do with future feature additions. Thus, these patches were difficult for the KDE developers to integrate back into KHTML.^[12] Furthermore, Apple had demanded developers to sign nondisclosure agreements before looking at Apple's source code and even then they were unable to access Apple's bug database.^{[citation needed]}

During the publicized 'divorce' period, KDE developer Kurt Pfeifle (pipitas) posted an article claiming KHTML developers had managed to backport many (but not all) Safari improvements from WebCore to KHTML, and they always appreciated the improvements coming from Apple and still do so. The article also noted Apple had begun to contact KHTML developers about discussing how to improve the mutual relationship and ways of future cooperation.^[13]

Since the story of the fork appeared in news, Apple has released changes of the source code of its KHTML fork in a CVS repository.^[14] Since the transfer of the sourcecode into a public CVS repository, Apple and KHTML developers have had increasing collaboration. Many KHTML developers have become reviewers and submitters for WebKit SVN repository.

The WebKit team had also reversed many Apple-specific changes in the original WebKit code base and implemented platform-specific abstraction layers to make committing the core rendering code to other platforms significantly easier.^[15]

In July 2007, the Ars Technica website published an article reporting that the KDE team would move from KHTML to WebKit.^[16] Instead, after several years of integration, KDE Development Platform version 4.5.0 was released in August 2010 with support for both WebKit and KHTML, and development of KHTML continues.^[17]

Open-sourcing[link]

On June 7, 2005, Safari developer Dave Hyatt announced on his weblog that Apple was open-sourcing WebKit (previously, only WebCore and JavaScriptCore were open source) and opening up access to WebKit's CVS tree and the bug Database tool.^[14] This was announced at Apple's Worldwide Developers Conference 2005 by Apple Senior Vice President of Software Engineering Bertrand Serlet.

In mid-December 2005 support for Scalable Vector Graphics was merged into the standard build^[18] and in early January 2006 the source code was migrated from CVS to Subversion.

WebKit's JavaScriptCore and WebCore components are available under the GNU Lesser General Public License, while the rest of WebKit is available under a BSD-style license.

Further development[link]

Beginning in early 2007, the development team began to implement Cascading Style Sheets (CSS) extensions, including animation, transitions and both 2D and 3D transforms;^[19] such extensions were released as working drafts to the World Wide Web Consortium (W3C) in 2009 for standardization.^[20]

In November 2007, the project announced that it had accomplished support for HTML5 media features, allowing for embedded video to be natively rendered and script-controlled in WebKit.^[21]

On June 2, 2008, the WebKit project announced they rewrote JavaScriptCore as "SquirrelFish", a bytecode interpreter.^[22][23] The project evolved into SquirrelFish Extreme (abbreviated SFX), announced on September 18, 2008, which compiles JavaScript into native machine code, eliminating the need for a bytecode interpreter and thus speeding up JavaScript execution.^[24] Initially the only supported architecture for SFX was the x86 architecture, but at the end of January 2009 SFX was enabled for Mac OS X on x86-64 architectures as it passes all tests on that platform.^[25]

WebKit2[link]

WebKit2 was announced on 8 April 2010. WebKit2 is designed from the ground up to support a split process model, where the web content (JavaScript, HTML, layout, etc.) runs in a separate process from the application UI. This model is similar to what Google Chrome now offers, with the major difference being that WebKit2 has built the process split model directly into the framework, allowing other clients to use it. Currently WebKit2 is available for Mac, Windows and MeeGo-Harmattan.^[26][27][28]

Use[link]

Usage share of web browsers according to StatCounter.

WebKit is used as the rendering engine within Safari on Windows, Mac OS X and iOS. Other applications on Mac OS X make use of WebKit, such as Apple's e-mail client Mail and the 2008 version of Microsoft's Entourage personal information manager, both of which make use of WebKit to render e-mail messages with HTML content.

New web browsers have been built around WebKit such as the S60 browser^[29] on Symbian mobile phones, Blackberry Browser (ver 6.0+), Midori, Shiira, Chrome browser,^[30][31] Uzbl, Maxthon 3, xxxterm, the Android Web browser, and the browser used in PlayStation 3 system software from version 4.10.^[32] KDE’s Rekonq web browser and Plasma Workspaces also use it as the native web rendering engine. WebKit has been adopted as the rendering engine in OmniWeb, iCab and Web (previously known as Epiphany) replacing their original rendering engines. Sleipnir started development for WebKit in its browser in 2012, and as of May 17, 2012, is in alpha 3 stages.^[33] Epiphany supported both Gecko and WebKit for some time, but the team decided that Gecko's release cycle and future development plans would make it too cumbersome to continue supporting it. HP's Palm WebOS uses WebKit as the basis of its application runtime. The latest interface update for Valve Corporation's Steam employs WebKit to render its interface and built-in browser.^[34] WebKit is used to render HTML and run JavaScript in the Adobe Integrated Runtime application platform. In Adobe Creative Suite CS5, WebKit is used to render some parts of the user interface. As of the first half of 2010, analyst estimates place the cumulative number of mobile handsets shipped with a WebKit-based browser at 350 million.^[35] WebKit will continue to dominate the mobile industry as the market penetration of smartphones, the engine's primary contributors, increases. The introduction of tablets will also be a contributing factor, since many tablets have the Android or Apple iOS operating system (iPad, iPad 2) installed. In 2011, from January to August, the market share of Android OS alone increased from 15% to 20%. Combining the increase of smartphone and tablet sales, coupled with the increasing market share of Chrome, WebKit could become the dominant web browser engine in 2012. Consider, for example, that for the period of January to September 2011, the market share of Google's Chrome browser went from 15% to 23.5%, and Safari maintained a 5-6% share while use of both Internet Explorer and Mozilla decreased significantly. As of February 2012^[update], WebKit's market share at 36%, is equal to the market share of the Trident/MSHTML engine used to power Internet Explorer.^[36] If this growth rate continues, total use of WebKit (Chrome, Safari, and smartphones/tablets) will surpass 50% by the end of 2012 and WebKit will lead in market share.^[37]

Ports[link]

The week after Hyatt's announcement of WebKit's open-sourcing, Nokia announced that it had ported WebKit to the Symbian operating system and was developing a browser based on WebKit for mobile phones running S60. Now named Web Browser for S60, it is used on Nokia, Samsung, LG, and other Symbian S60 mobile phones. Apple has also ported WebKit to the iOS to run on the iPhone, iPod Touch and iPad, where it is used to render content in the device's web browser and e-mail software.^[38] The Android mobile phone platform uses WebKit as the basis of its web browser^[39] and the Palm Pre, announced January 2009, has an interface based on WebKit.^[40] The Amazon Kindle 3 includes an experimental WebKit based browser.^[41]

In June 2007, Apple announced that WebKit had been ported to Microsoft Windows as part of Safari. There are also ongoing ports for the open source operating systems Syllable,^[42] Haiku^[43] and AROS Research Operating System (AROS).^[44]

WebKit has also been ported to several toolkits that support multiple platforms, such as the GTK+ toolkit,^[45][46] Qt framework,^[47] Adobe Integrated Runtime, Enlightenment Foundation Libraries (EFL), and the Clutter toolkit.^[48] Qt Software (owned by Nokia) includes the Qt port in the Qt 4.4 release. The Qt port of WebKit is also available to be used in Konqueror in KDE 4.1.^[16] The Iris Browser on Qt also uses WebKit. The Enlightenment Foundation Libraries (EFL) port is under development (by Samsung and ProFUSION) focusing the embedded and mobile systems, for use as stand alone browser, widgets/gadgets, rich text viewer and composer. The Clutter port is developed by Collabora and sponsored by Bosch.

There is also a project synchronized with WebKit (sponsored by Pleyo)^[49] called Origyn Web Browser, which provides a meta-port to an abstract platform with the aim of making porting to embedded or lightweight systems quicker and easier.^[50] This port is used for embedded devices such as set-top boxes, PMP and it has been ported into AmigaOS,^[51][52] AROS^[53] and MorphOS. MorphOS version 1.7 is the first version of Origyn Web Browser (OWB) supporting HTML5 media tags.^[54][55]

Components[link]

WebCore[link]

WebCore is a layout, rendering, and Document Object Model (DOM) library for HTML and SVG, developed by the WebKit project. Its complete source code is licensed under the GNU Lesser General Public License (LGPL). The WebKit framework wraps WebCore and JavaScriptCore, providing an Objective-C application programming interface to the C++-based WebCore rendering engine and JavaScriptCore script engine, allowing it to be easily referenced by applications based on the Cocoa API; later versions also include a cross-platform C++ platform abstraction, and various ports provide additional APIs.

WebKit passes the Acid2 and Acid3 tests, with pixel-perfect rendering and no timing or smoothness issues on reference hardware.^[56]

JavaScriptCore[link]

JavaScriptCore is a framework that provides a JavaScript engine for WebKit implementations, and provides this type of scripting in other contexts within Mac OS X.^[8][57] JavaScriptCore is originally derived from KDE's JavaScript engine (KJS) library (which is part of the KDE project) and the PCRE regular expression library. Since forking from KJS and PCRE, JavaScriptCore has been improved with many new features and greatly improved performance.^[58]

On June 2, 2008, the WebKit project announced they rewrote JavaScriptCore as "SquirrelFish", a bytecode interpreter.^[22][23] The project evolved into SquirrelFish Extreme (abbreviated SFX, marketed as Nitro), announced on September 18, 2008, which compiles JavaScript into native machine code, eliminating the need for a bytecode interpreter and thus speeding up JavaScript execution.^[24]

Drosera[link]

Drosera is a JavaScript debugger that was included with the nightly builds of WebKit.^[59][60] It was named after Drosera, a genus of carnivorous plants. Drosera has been replaced by the inclusion of debugging functions in the Web Inspector.^[61]

See also[link]

Free software portal

• Comparison of layout engines
• List of KHTML-based browsers
• List of WebKit-based browsers
• List of graphical layout engines

References[link]

External links[link]

• Official website
• The WebKit Help Mailinglist Archive – WebKit Help mailinglist archive
• SunSpider 0.9.1 JavaScript Benchmark

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